Ageism is rife in this world, it's never been anything serious (since I have the advantage of being 6ft3 and well built) but when I was younger I used to get a lot of mouth from people older than me.
Particularly when I handle advice it was a problem, since I was an agony uncle a lot of people refused to go to me because I was too young, took my age off the forum and suddenly people didn't care anymore. Yay for prejudices.
But yeah, never anything really bad to be honest. I got it pretty lucky in terms of prejudice. White, middle class (eh, kinda. Family was working class and brought themselves up, guess it counts), well educated, tall, relatively well built, symmetrically featured, straight as a whistle, male...yup I've got it pretty good.
Oh I've had some sexism too, man flu? Yes the one time I'm ill in some four years it's being faked. Feeling depressed? Oh get over it, it's not like you have a period to deal with and so on.
Again nothing major but little niggles which shouldn't be there.